[PATCH] D43968: [X86] Handle EAX being live when calling chkstk for x86_64

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo created this revision.
mstorsjo added reviewers: craig.topper, chapuni.
Herald added subscribers: JDevlieghere, aprantl.

EAX can turn out to be alive here, when shrink wrapping is done (which is allowed when using dwarf exceptions, contrary to the normal case with WinCFI).

This fixes PR36487.


Repository:
  rL LLVM

https://reviews.llvm.org/D43968

Files:
  lib/Target/X86/X86FrameLowering.cpp


Index: lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- lib/Target/X86/X86FrameLowering.cpp
+++ lib/Target/X86/X86FrameLowering.cpp
@@ -1213,30 +1213,34 @@
     bool isEAXAlive = isEAXLiveIn(MBB);
 
     if (isEAXAlive) {
-      // Sanity check that EAX is not livein for this function.
-      // It should not be, so throw an assert.
-      assert(!Is64Bit && "EAX is livein in x64 case!");
-
-      // Save EAX
-      BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
-        .addReg(X86::EAX, RegState::Kill)
-        .setMIFlag(MachineInstr::FrameSetup);
+      if (Is64Bit) {
+        // Save RAX
+        BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH64r))
+          .addReg(X86::RAX, RegState::Kill)
+          .setMIFlag(MachineInstr::FrameSetup);
+      } else {
+        // Save EAX
+        BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
+          .addReg(X86::EAX, RegState::Kill)
+          .setMIFlag(MachineInstr::FrameSetup);
+      }
     }
 
     if (Is64Bit) {
       // Handle the 64-bit Windows ABI case where we need to call __chkstk.
       // Function prologue is responsible for adjusting the stack pointer.
-      if (isUInt<32>(NumBytes)) {
+      int Alloc = isEAXAlive ? NumBytes - 8 : NumBytes;
+      if (isUInt<32>(Alloc)) {
         BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
-            .addImm(NumBytes)
+            .addImm(Alloc)
             .setMIFlag(MachineInstr::FrameSetup);
-      } else if (isInt<32>(NumBytes)) {
+      } else if (isInt<32>(Alloc)) {
         BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri32), X86::RAX)
-            .addImm(NumBytes)
+            .addImm(Alloc)
             .setMIFlag(MachineInstr::FrameSetup);
       } else {
         BuildMI(MBB, MBBI, DL, TII.get(X86::MOV64ri), X86::RAX)
-            .addImm(NumBytes)
+            .addImm(Alloc)
             .setMIFlag(MachineInstr::FrameSetup);
       }
     } else {
@@ -1251,10 +1255,14 @@
     emitStackProbe(MF, MBB, MBBI, DL, true);
 
     if (isEAXAlive) {
-      // Restore EAX
-      MachineInstr *MI =
-          addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm), X86::EAX),
-                       StackPtr, false, NumBytes - 4);
+      // Restore RAX/EAX
+      MachineInstr *MI;
+      if (Is64Bit)
+        MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV64rm), X86::RAX),
+                          StackPtr, false, NumBytes - 8);
+      else
+        MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm), X86::EAX),
+                          StackPtr, false, NumBytes - 4);
       MI->setFlag(MachineInstr::FrameSetup);
       MBB.insert(MBBI, MI);
     }


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